Mandrels have been used to make rigid tubular articles. The rigid tubular articles have been made by placing the material that will form the tubular article about the mandrel, and hardening that material to a rigid state. After the tubular article becomes rigid, the mandrel is removed from the interior of the tubular article.
Removal can be accomplished by sliding the mandrel out from the interior of the tubular article. This method works well when the tubular article does not have a complex shape. For instance, if the tubular article is straight, or if it is arcuate with a constant bend radius, the mandrel can be slid out from the interior of the tubular article.
A conventional mandrel comes in one piece, and has an outer shape that corresponds to the shape of the interior of the tubular article. It has been problematic to use a single conventional mandrel to form a rigid tubular article that has both a straight portion and an arcuate portion. When the rigid tubular article has such a shape, it is difficult to separate the rigid tubular article from the mandrel. The combination of the straight and arcuate portions prevents the mandrel from being slid out of the interior of the rigid tubular article. Rigid tubular articles having straight and arcuate portions therefore cannot be formed from a single conventional mandrel.
To make a tubular article having a straight portion and an arcuate portion from a conventional mandrel, the article can be made by using more than one mandrel: one mandrel is used to form the straight portion; and another is used to form the arcuate portion. The individual tubular segments formed from each of the separate mandrels are subsequently connected to each other to produce the desired tubular article.
Rigid tubular articles having straight and arcuate portions can be made from "wash-away" mandrels. In this instance, the mandrel can be remove from the interior of the rigid tubular article by dissolving the mandrel with steam. Templemen Industries, Inc. of North Chicago, Ill. markets such a mandrel. "Wash-away" mandrels, however, are disadvantageous in that the mandrel is not reusable, and it leaves a dissolved by-product that must be disposed of in an environmentally sound manner.